(1) Field of the Invention
The present invention relates to an apparatus for inspecting an illumination device, and in particular, to a technology that is effective when applied to an apparatus for inspecting a backlight used in a liquid crystal display device when turned on.
(2) Description of the Related Art
Some liquid crystal display devices have an illumination device, which is referred to as a backlight, provided behind the liquid crystal display panel (at the rear).
The backlights convert light emitted from a light source, such as LEDs or a fluorescent lamp, into rays emitted from an area so that the liquid crystal display panel can be illuminated, and various structures of backlights are known. In addition, backlights are usually formed of a number of optical sheets that are layered on top of each other in order to increase the degree of symmetry of the rays from an area (uniformity of the brightness in an area) or the efficiency of the use of light for illuminating the liquid crystal display panel, for example. These optical sheets include a prism sheet, a light diffusing sheet and the like, and a combination of these is determined by the type of or the way of arranging the light source, the properties required for the liquid crystal display device and the like.
The backlights used for a liquid crystal display device are usually inspected when turned on before they are combined with a liquid crystal display panel. Through this inspection when turned on, the degree of symmetry of the rays from an area (uniformity in the brightness of an area) and whether or not any foreign substance is between the optical sheets are checked. Such an inspection when turned on may be carried out on a backlight to which a light source has already been attached by turning on the light source or may be carried out on a backlight to which a light source has not yet been attached by temporarily attaching a light source for inspection.